1. Field of the Invention
The present invention relates to a method of manufacturing a molded plastic product with a pad.
2. Description of the Related Art
Molded plastic products having pads are used for various purposes including car interior parts and furniture.
FIG. 6 shows a car instrument panel as an example of the molded plastic products. The panel is made of a core 41 and a pad 42. The pad 42 is attached to a part of the surface of the core 41. Some products have a pad that entirely covers the surface of a core.
A monolithic molding technique is a simple technique to manufacture a molded plastic product having a pad. This technique forms a foam body that adheres to a skin to make a pad. At the same time, the foam body adheres to a core, so that the pad, and core are integrated into a product.
FIG. 7 shows an example of the monolithic molding technique. A core 53 has a sidewall 51 surrounding a pad housing 52. The core 53 is set on an upper mold 61. A skin 72 to form a pad has a side face 71. The skin 72 is set on a lower mold 62 so that the side face 71 is in contact with the sidewall 51 of the pad housing 52. A foam ingredients P is activated to produce foam between the core housing 52 and the skin 72, to integrate them into one body.
FIG. 8 is an enlarged section showing an essential part of FIG. 7. The foam produced by the foam ingredients P fills a space between the core 53 and the skin 72. The pressure generated by foaming of the foam ingredients presses the side face 71 against the sidewall 51 as indicated with a dotted line, thereby preventing the foam from oozing onto the surface of the skin 72. The foam ingredients P, skin 72, and core 53 are solidified together due to the self-adhesive property of the foam ingredients P.
This prior art, however, has some problems. The side face 71 of the skin 72 has low rigidity because of a free end 73. The side face 71 is easily deformed or corrugated during storage or on the lower mold 62. Once the side face 71 is deformed, it causes a gap S with respect to the sidewall 51 of the core 53 as shown in FIG. 9. Then, the foam ingredients P may ooze onto the surface of the skin 72, to spoil the appearance of the product or cause unfilledspots in the pad. In FIG. 6, the pad 42 is arranged at a part of the surface of the core 41 (corresponding to the core 53 of FIG. 8). If the foam ingredients leaks through a boundary 43 onto the surfaces of the core 41 and pad 42, the appearance of the instrument panel is spoiled.
The deformed side face 71 will not restore to its original shape even if the skin 72 is heated. This problem is difficult to solve.